lo A TEXT-BOOK OF BOTANY. 



brown gelatinous stratum, this arrangement due to the cell divid- 

 ing in all directions. They occur on moist earth, stones, wharf 

 pilings, and even on window panes of greenhouses, thus being 

 distributed in both fresh- and salt-water regions. They some- 

 times form a kind of crustaceous stratum, and sometimes soft, 

 slimy masses sufficiently abundant that they can be stripped by the 

 handful from dripping, partially shaded rocks. Owing to the 

 variation in color and general habit of the plant a great many 

 species have been described, but up to the present time about 60 

 have been sharply distinguished. 



Oscillatoria, formerly known as Oscillaria, is the name applied 

 to a simple filamentous blue-green alga (Fig, 6) that is char- 

 acterized by movement from side to side as in a pendulum, due, 

 as has been suggested, to the movement of spiral masses of proto- 

 plasm extending from cell to cell. These filaments consist of a 

 series of disk-shaped cells like a pile of coins placed side by side, 

 the end cell being rounded ofif and more or less convex. The con- 

 tents are made up of a finely granular substance differentiated 

 into two areas, a dark central nuclear portion, and a peripheral 

 holding the pigment, which may vary from a bluish-green to dark 

 olive-green or even red sufficiently intense to give the water a 

 red color. The filaments vary from o.ooi to 0.005 mm. in diame- 

 ter, though they may attain a size of 0.050 mm. 



Oscillatoria is usually found on wet, marshy grounds, in 

 ditches among decayed vegetable matter, on wood subject to hot 

 waste from steam engines, around pumps and cisterns, and in 

 greenhouses. It occurs in fresh and salt water. 



Lyngbya somewhat resembles Oscillatoria, but does not show 

 any oscillations and the filaments are each provided with a dis- 

 tinct sheath (Fig. 6). It forms late in the summer in large tufts. 

 It is of a bluish-green color, forms long filaments, occurring in 

 the late summer upon Zostera and other Algse. The groups are 

 large and characteristic and have been given the common name 

 Alermaid's Hair. The cells are about 0.030 mm. in diameter. 



Uroglena is a form which is more or less oval or pear-shaped, 

 about 0.014 to 0.018 mm. in length, and extended into a stalk below, 

 the upper end being provided with two unequal cilia (Fig. 6). 

 The wall secretes a large amount of mucilage. The organisms 



